Fish ladders have been provided heretofore and generally are comprised of a series of boxes positioned adjacent one another in an incrementally elevated fashion, in a stepped or ladder configuration that allows fish to migrate from one box to an upstream box. The series of boxes includes a flow inlet above an obstruction, e.g., waterfall or dam, in a waterway and a flow outlet below the obstruction. Typically the inlet is elevated from the level of the outlet so that water from the waterway will flow through the fish ladder from the inlet to the outlet. In this manner, water will flow into the uppermost box of the fish ladder, then cascade down the series of boxes to the outlet. The boxes become filled with water and, therefore, provide a series of incrementally elevated pools extending from the outlet to the inlet. Fish utilizing such a fish ladder can jump from the flow outlet into the first pool, from the first pool into the second pool, and so on, until the flow inlet is reached. At that point, the fish will be above the obstruction and can continue upstream along the waterway to its destination. Fish ladders of the foregoing nature have been in use for a considerable length of time, and are generally thought to provide an adequate alternate path for fish to use to negotiate around an obstacle in a waterway. However, such apparatuses also have a number of disadvantages and shortcomings that render them less attractive to fish and expensive to maintain.
One such disadvantage is that the boxes retain a considerable amount of sediment due to the nature of the flow of water into and out of each box. It will be appreciated that the buildup of sediment in the box is a significant disadvantage because a box that is filled with sediment may only provide a very shallow pool for the fish or, at times, no pool at all. Furthermore, during high water conditions, for example in the spring or after significant rainfall, the water carries a large amount of sediment that settles in and fills the boxes. This is, of course, detrimental to the fish migrating along the waterway that would use the fish ladder. As such, workers spend many thousands of hours each year removing sediment from the boxes of the fish ladders.
Additionally, it is well understood that fish need a certain minimum amount of water flowing along a waterway to be able to swim therealong, and that fish are naturally attracted to waterways having higher relative flow rates. These known ladders typically provide a relatively low amount of water flow during normal and low water level conditions. As such, the fish may not be attracted to the water flowing through the conventional fish ladder resulting in reduced use of the ladder by migrating fish.
Another function or feature of a fish ladder is to provide pools in which the fish can rest while advancing up the fish ladder from the lower level of the outlet to the elevated level of the inlet. During high water periods, the flow of water along the fish ladder does not cascade from box to box. Rather, the water rushes along the fish ladder creating turbulence and water currents flowing in the pools reducing the area in which the fish can rest and often times washing the fish back down the ladder to the lower level of the outlet.
Another disadvantage of existing fish ladders is the area that is commonly required to construct a conventional fish ladder formed of cascading boxes. In many situations, the fish ladder is constructed in an open area in which equipment and personnel can work. However, in other situations where a fish ladder would otherwise be desirable, the construction thereof is not possible due to space or access limitations, such as through a culvert running beneath a roadway, for example.